Continuous operation compressor system



June 28, 1966 J. E. MALONEY 3,257,819

OONTINUOUs OPERATION COMPRESSOR SYSTEM Filed Sept. 26, 1963 2 Sheets-Sheet l powarz. SUPPLY co N DEN SER.

22 COMPRESSOR l0 INVENTOR. JAMas E MALONEY ATTORNEYS June 28, 1966 J. E. MALONEY CONTINUOUS OPERATION COMPRESSOR SYSTEM Filed Sept. 26, 1963 2 Sheets-Sheet 2 INVENTOR. JAMES E. MALONEY .mm. Rm 3 dowwmdnzz 00 W QW dMWZWOZOU TJOBDW BMZIOQ ATTORNEYS a predetermined temperature.

United States Patent 3,257,819 CONTINUOUS OPERATION COMPRESSOR SYSTEM James E. Maloney, Blissfield, Mich, assignor to Blissfield Manufacturing Company, Blissfield, Mich, a corporation of Michigan Filed Sept. 26, 1963, Ser. No. 311,688 8 Claims. (Cl. 62-499) The present invention relates as indicated to a refrigeration system wherein the compressor runs continually and the compressed refrigerant is caused to completely bypass the evaporator when cooling of the evaporator is not desired; and more particularly to a system of the above described type wherein the product of the rate of mass flow of refrigerant through the compressor and the pressure differential across the compressor during periods when cooling is not desired in the evaporator -is caused to be considerably less than when the refrigerant is caused to flow through the evaporator.

As a result of a study of the breakdowns in small hermetically sealed refrigeration systems of the type wherein the electrical drive motor is housed within a shell containing the refrigerant, it was found that approximately 75% of the breakdowns occurred by reason of failure of the electrical starting windings of the motor. The starting windings of electrical motors are designed to carry high current densities for short periods of time in order that the size of the windings can be kept to a minimum. The starting windings therefore heat up rapidly at a time when the motor is started, and at a time when substantially no flow of refrigerant through the motor exists. Shortly thereafter the flow of electricity to the starting windings is cut off and a flow of cool refrigerant gases from the evaporator reaches the starting windings to suddenly drop the temperature of the starting windings. The insulation 'on the starting windings is therefore subjected to a thermal shock each time that the compressor is started, with the result that cracks in the insulation eventually develop to short out the starting windings.

A further difliculty occurs by reason of stopping and starting of the compressor in that oil runs out of the bearings when the compressor is stopped. Immediately on start up therefore, metal to metal contact in the bearings sometimes occurs with the result that a high degree of bearing wear is also experienced in compressors and in the motors of hermetically sealed units which are frequently stopped and started.

It has been proposed heretofore to provide refrigeration systems wherein the compressor runs continually and to' bypass the flow of refrigerant around the evaporator when the evaporator has produced a temperature which is below Such systems have had approximately the same power consumption during the time that the system was not producing a cooling effect in the evaporator as the system has had when a cooling eifect was produced in the evaporator. Inasmuch as such systems may produce a cooling effect in the evaporator for less than fifty percent of the time, prior art continuously operated compressor systems have not been economical to operate.

An object of the present invention is the provision of a new and improved refrigeration system wherein the compressor continually functions normally to produce a Patented June 28, 1966 refrigerant flow even during times that evaporator cooling does not take place and which is economical to operate.

A more particular object of the invention is the provision of a new and improved refrigeration system of the immediately above-mentioned type, and wherein the coma compressor which normally discharges through a condenser and evaporator back to the suction of the compressor at a predetermined mass rate of flow when evaporator cooling is desired, and which when evaporated cooling is not desired, causes the compressor to function normally but to discharge through a by-pass back to its suction, said by-pass having a greater resistance to flow than does the normal flow path through the evaporator to thereby reduce the mass rate of refrigerant flow through the compressor when evaporator cooling-is not desired.

A further object is the provision of a refrigeration system of the above described type in which the by-pass takes the discharge from the condenser and passes it through a heat transfer surface in contact with the condenser or other heat source to transfer heat therebetween in just sufficient amount to vaporize liquid flowing through the by-pass and prevent it.from entering the suction of the compressor.

Further objects and advantages will become apparent to those skilled in the art to which the invention relates from the following description of several preferred em- FIG. 2 is a diagrammatic view similar to FIG. 1 showing another embodiment of refrigeration system.

The refrigeration system shown in FIG. 1 generally comprises a hermetically sealed motor and compressor unit 10 of the type in which the refrigerant gases flowing to the suction of the compressor pass through the starting and running windings of the motor. sure discharge gases from the compressor unit 10 are con.- ducted through conduit 11 to a condenser 12 where heat is transferred to the surrounding atmosphere and the refrigerant gases are condensed to a liquid. Liquid from the condenser 12 passes through a conduit 13 to a junction point 14 with a by-pass conduit 15.

During the cooling cycle of the refrigeration system shown, flow through the by-pas's conduit 15 is prevented by a shut-off valve 16. Liquid refrigerant flow from the junction point 14 normally passes through a shut-off valve 17 which is open during the cooling cycle to permit flow througha fiow restriction or throttling device 18 which reduces the pressure on the refrigerant and causes it to V flash into a vapor. The shut-off valves 16 and 17, shown,

are normally closed valves, and are opened upon energi- The hot high pres-.

where liquid refrigerant picks up heat from the evaporator and changes to a vapor. The vapor from the evaporator 21 returns to the compressor 10 through suction line 22 and the process is repeated.

The above described refrigerant flow through the compressor 10, condenser 12 and evaporator 21 continues until the temperature of the evaporator 21, or a temperature which the evaporator 21 controls, reaches a predetermined low level or set temperature. In the embodiment shown, a temperature sensing bulb 23 is located in contact with the evaporator 21. Vapor pressure from the bulb 23 is transmitted through capillary tubing 24 to the switch 25 to hold the blade 26 against contact 27 to energize solenoid 20 so long as the temperature of the evaporator is above a set temperature. When the temperature of the evaporator drops below the set temperature, vapor pres sure from bulb 23 is sufliciently low that the blade 26 is snapped by structure, now shown, into engagement with contact 28. This de-energizes solenoid 20 to allow valve 17 to close and energizes solenoid 19 to open valve 16 and start the non-cooling cycle.

During the non-cooling cycle, the compressor 10 pumps continuously through the condenser 12 and line 13, as it did during the cooling cycle, but the refrigerant flow is now diverted through now open valve 16, through a flow restriction 29, to a reheat coil 30 that is embedded in the condenser 12 to absorb heat therefrom. Fluid from the flow restriction 29 picks up heat in the reheat coil 30 to vaporize all of its liquid to vapor, and the vapor from the reheat coil 30 is transmitted through return line 31 to the suction lines 22 of the compressor. The flow restriction 29 is sized to provide a considerably greater resistance to flow than does the flow restriction 13, so that the mass rate of refrigerant pumped by the compressor during the non-cooling cycle is considerably less than during the cooling cycle. The power supply circuit for the motor of the compressor will contain a manually actuated stop-start switch 32 which stays closed except when the unit is to be taken out of service, and does not contain a switch which is open and closed in response to the temperature of the evaporator itself, or of a temperature which the evaporator controls.

In one refrigeration system of the type shown in FIG. 1 which has been built and tested, a tube 126 inches long and having a cylindrical flow passage of 0.040 inch ID. was used for the flow restriction 18. A tube 96 inches long and having a cylindrical flow passage of 0.026 inch ID. was used for the flow restriction 29. When the valve 16 was shut and the valve 17 was open to produce flow through the evaporator 21, the pressure in conduit 11 at the discharge of the compressor was 145 p.s.i.g., the pressure in conduit 22 at the suction of the compressor was 19 p.s.i.g., and the /s H.P. motor driving the compressor drew 200 watts. When the system was on the non-cooling cycle, with the valve 17 closed and valve 16 open, the pressure in conduit 11 at the compressor discharge was 120 p.s.i.g., the pressure in conduit 22 at the compressor suction was 2 p.s.i.g., and the motordriving the compressor drew 140 watts. The rate of fluid displacement of the compressor 10 during the non-cooling cycle was as great as during the cooling cycle, but because the pressure at the compressor suction was less during the non-cooling cycle, the mass rate of flow handled by the compressor during the non-cooling cycle was less than the mass rate of flow during the cooling cycle. Because the mass rate of flow of refrigerant through the compressor was less during the non-cooling" cycle than it was during the cooling cycle, the power consumption of the compressor was less during the noncooling cycle than during the cooling cycle.

Because the compressor of the refrigeration system of the present invention runs continuously, it has been found that a H.P. unit can handle the same heat load as a H.P. unit run on a conventional cycle where the compressor is stopped during the non-cooling cycle.

The result is that the system shown in FIG. 1 having a /5 H.P. motor-compressor unit that is run continuously has about the same power consumption as a conventional H.P. unit that is stopped and started to handle the same heat load, but the system of the present invention has considerably less mechanical and electrical failures.

The embodiment of refrigeration system shown in FIG. 2 ditfers from the embodiment of refrigeration system shown in FIG. 1 in that the system of FIG. 2 by-passes compressor discharge gases directly back into the compressor suction during the non-cooling cycle, instead of passing them through a condenser and reheat coil. The system shown in FIG. 2 comprises a hermetically sealed compressor and motor unit 40 of the same type shown in FIG. 1. The discharge from the compressor unit 40 passes through discharge conduit 41 to a T connection 42, one side of which is normally closed off by a shut-off valve 43 that is normally closed, and the other side of which communicates with a check valve 44. Refrigerant flow during the norm-a1 or cooling cycle of the system passes through the check valve 44 to a condenser 45 where high pressure refrigerant gases are condensed to a liquid. Liquid from the condenser 45 passes through a flow throttling means 46 from which the fluid is communicated to the evaporator 47 through conduit 48. Liquid refrigerant in the evaporator 47 picks up heat to change into a vapor, and the vapor from the evaporator 47 passes through conduit 49, and now open shut-off valve 50 to the suction conduit 51 of the compressor. The shut-off valve 50 is a normally closed valve which is opened during the cooling cycle by a solenoid 52. The compressor 40- continues to recirculate refrigerant through the above-described system until the temperature of the evaporator 47, or a temperature which the evaporator 47 controls decreases to a set temperature. For reasons which will later be explained, the system is preferably controlled by a temperature sensing element 53 which senses the temperature of the evaporator structure adjacent the end from which the refrigerant discharges. The temperature sensing element 53 shown is a vapor pressure bulb whose vapor pressure is transmitted through tube 54 to a temperature control 55 having a switch blade 56 that engages a contact 57 when the temperature sensed by the bulb 53 is above a set temperature, and which is moved to engage a contact 58 when the temperature sensed by the bulb 53 falls below the set temperature. The temperature control 55 is preferably also of the type which lowers the set temperature at which the blade 56 moves from contact 57 to 58 as the ambient temperature increases. When the temperature of the evaporator 47 is above the set temperature of the temperature control 55, the blade 56 engages contact 57 to energize solenoid 52 to hold open the shut-off valve 50 and allow refrigerant flow through the evaporator 47.

When the temperature of the evaporator 47 decreases below the set temperature of the temp-control 55, the blade 56 moves out of engagement with contact 57 to allow valve 50 to close, and shortly thereafter the blade engages contact 58. The contact 58 is connected through pressure control 59 to a solenoid 60 which when energized opens valve 43. When the temperature of the evaporator 47, therefore, is below the set temperature, the high pressure discharge gases from the compressor pass through valve 43 to a flow restricting device 61 through a by-pass line 62 to the suction line 51 of the compressor. At temperatures of the evaporator 47 below the set temperature, therefore, the compressor discharge by-passes both the condenser 45 and evaporator 47 and returns directly to the suction of the compressor 40. The flow restriction 61 preferably offers a greater resistance to flow than does the flow restriction 46, so that the suction to the compressor drops durings the non-cooling cycle and the mass rate of fiow through the compressor is thereby decreased from the mass rate of flow during the cooling cycle.

It is preferable that a time delay exists between the closing of valve 50 and the opening of valve 43 so that refrigerant trapped between the two valves 43 and 50 is evacuated and pumped to the discharge side of the compressor 40. It is also preferable that the volume of the system between the discharge of the compressor and the shut-off valve 43 and check valve 44 be as small as possible so that most of the refrigerant is forced through the checkv-alve 44 and is trapped between the check valve 44 and shut-off valve 50 at the time valve 43 opens. This will cause a considerable drop in the back pressure on the compressor when valve 43 opens without causing an appreciable rise in the suction pressure to the compressor. This, therefore, greatly reduces the mass rate of flow of refrigerant through the compressor during the non-cooling cycle and at the same time reduces the discharge pressure of the compressor to some extent resulting in a large drop in power consumption during the non coolin cycle from the Power consumption during the cooling cycle.

If refrigerant is recirculated through the bypass line 62 over an extended period of time, it is possible thatthe temperature of the compressor will rise excessively. As previously stated, it is preferable that the temperature sensing element 53 sense the temperature of the heat transfer surface adjacent the refrigerant exit end. The evaporator usually has a heat capacity considerably smaller than that of the load which it cools. By sensing which energizes solenoid 60 to engage contact 65 that is connected to solenoid 52. This actuation of pressure control 59 causes valve 43 to close the bypass conduit 62 and open shut-off valve 50 to change the system back to its normal cooling cycle. Cool refrigerant from the evaporator 47 then enters the compressor to reduce its temperature while the discharge of the compressor passes through the condenser 45 and evaporator 53 to be recirculated through the compressor until the temperature of the compressor drops to its normal level. The pressure control 59 then changes back to its normal condition with its switch blade 63 in engagement with contact 64 to again place the system under the control of the temperature control 55.

The power supply for the compressor 40 also contains a manually actuated stop-start switch 66 which is not used as a temperature control device but is only opened by the operator to take the system out of operation. During the non-cooling cycle when the valve 43 is opened and the shut-off valve 50 is closed, the mass rate of flow through the compressor 40 is reduced to a' rate that is less than the mass rate of flow through the compressor of FIG. 1, so that the system of FIG. 2 has less power consumption than does the system of FIG. 1.

In systems where the volume of the system between the compressor discharge and valves 43 and 44 is very small, it may be possible to eliminate the flow restriction 61 entirely since the pressure drop across the compressor will be reduced in this instance to such a small value that the power consumption of the compressor during the non-cooling cycle will be low. Allowing valve 43 to remain closed for a short period of time --after valve 50 closes will also aid in reducing power consumption during the non-cooling cycle, since it causes refrigerant to be displaced out of the recirculating system used in the noncooling, cycle to thereby decrease the diiferential pressure across the compressor as well as the mass rate of flow through the compressor.

While the invention has been described in considerable detail, I do not wish to be limited to the particular embodiments shown and described, and it is my intention to cover hereby all novel adaptations, modifications, and arrangements thereof, which come within the practice of those skilled in'the art to which the invention relates.

What I claim is:

1. In a refrigeration system having a normally continuously operating compressor, drive means for said compressor, stop-start means for said drive means which is normally operable to cause said compressor to be actument comprising: by-pass conduit means for directing refrigerant from the discharge side of the compressor ahead of the evaporator to the suction of the compressor by-passing the evaporator, sensing means responsive to a temperature controlled by said evaporator, said sensing means being in a normal condition when said temperature controlled by said evaporator is above a predetermined temperature and being in another condition when said temperature controlled by said evaporator is below a predetermined temperature, flow diverting means having a normal condition, for communicating refrigerant from the discharge of the compressor through said evaporator and having another condition for substantially shutting off flow of refrigerant through said evaporator and diverting the flow through said by-pass conduit means, said flow diverting means being in the normal condition when said sensing means is in its normal condition and being in its other condition when said sensing means is in its other condition, and means effective when said flow diverting.

means is in its other condition and said stop-start means is in the normal condition and said compressoris driven by said drive means to reduce the product of the differential pressure across the compressor times the rate of mass flow of refrigerant through the compressor substantially below the predetermined product.

2. In a refrigeration system having a normally continuously operating com-pressor, drive means for said compressor, stop-start means [for said drive means which is normally operable to cause said compressor to be actuated,

a condenser, flow restricting means, an evaporator, and.

conduit means for directing a refrigerant from the discharge of the compressor through the condenser, the flow restricting means, the evaporator and back to the suction of the compressor, said condenser, said flow restricting means, said evaporator and said conduit means being effective, when said stop-start means is in the normal condition and said compressor is driven by said drive means, to provide a predetermined rate of mass flow of refrigerant through said evaporator, the improvement comprising: by-pass conduit means for directing refriger ant from the discharge side of the compressor ahead of the evaporator to the suction of the compressor by-passing the evaporator, sensing means responsive :to a temperature controlled by said evaporator, said sensing means being in a normal condition when said temperature controlled by said evaporator is above a predetermined temperature and being in another conditions when said temperature controlled by said evaporator is below a predetermined temperature, flow diverting means having a normal condition (for communicating refrigerant from the discharge of the compressor through said evaporator and having another condition for substantially shutting off flow of refrigerant through said evaporator and diverting the flow through said by-pass conduit means, said flow diverting means being in its normal condition when said sensing means is in its normal condition and being in its other condition when said sensing means is in its other condition, and means effective when said flow diverting means is in its other condition and said stop-start means is in the normal condition and said compressor is driven by said drive means to reduce the rate of mass flow of refrigerant through said by-pass means substantially below the predetermined rate of mass flow of refrigerant.

3. In a refrigeration system having a normally continuously operating compressor, drive means for said compressor, stop-start means for said drive means which is normally operable to cause said compressor to be actuated, a condenser, flow restricting means, an evaporator, and conduit means for directing a refrigerant from the discharge of the compressor through the condenser, the flow restricting means, the evaporator and back to the suction of the compressor, said condenser, said flow restricting means, said evaporator and said conduit means being effective, when said stop-start means is in the normal condition and said compressor is driven by said drive means, to provide a predetermined rate of mass flow of refrigerant through said evaporator, the improvement comprising: lby-pass conduit means for directing refrigerant from the downstream side of the condenser ahead of the evaporator to the suction of the compressor bypassing the evaporator, said by-pass conduit means including pressure restricting means effective to limit the rate of mass flow to said compressor substantially below the predetermined rate of mass flow which normally passes to said compressor through said flow restricting means, sensing means responsive to a temperature controlled by said evaporator, said sensing means being in a normal condition when said temperature controlled by said evaporator is above a predetermined temperature and being in another condition when said temperature controlled by said evaporat-or is below a predetermined temperature, flow diverting means having a normal condition for communicating refrigerant from the discharge of the compressor through said evaporator and having another condition for shutting off flow of refrigerant through said evaporator and diverting the flow through said by-pass conduit means, said flow diverting means being in its normal condition when said sensing means is in its normal condition and being in its other condition when said sensing means is in its other condition, whereby, when said stop-start means is in the normal condition, said compressor pumps refrigerant continually both during the time that refrigerant flows through the evaporator and during the time that flow is diverted from the evaporator, and the rate of mass flow of refrigerant through the compressor when flow is diverted from the evaporator is substantially less than the rate of mass flow of refrigerant through the compressor when the refrigerant passes through the evaporator.

42-. An improved refrigeration system as claimed in claim 2 wherein said by-pass conduit means includes means for vaporizing liquid that is effective to absorb heat from said condenser.

5. In a refrigeration system having a normally continuously operating compressor, drive means for said compressor, stop-start means for said drive means which is normally operable to cause said compressor to be actuated, a condenser, flow restricting means, an evaporator, and conduit means for directing 'a refrigerant from the discharge of the compressor sequentially through the condenser, the flow restricting means, the evaporator and back to the suction of the compressor, said condenser, said flow restricting means, said evaporator and said conduit means being effective, when said stop-start means is in the normal condition and said compressor is driven by said drive means, to provide a predetermined rate of mass flow of refrigerant through said evaporator, the improvement comprising: a first shut-off valve in said conduit means downstream of said condenser for preventing flow of refrigerant through said evaporator, bypass conduit means for directing refrigerant from the discharge of the compressor ahead of said first shut-oif valve to the suction of the compressor downstream of said evaporator, said bypass conduit means including pressure restricting means effective to limit the rate of mass flow to said compressor substantially below the predetermined rate of mass flow which normally passes to said compressor through said flow restricting means, a second shut-off valve in said by-pass conduit means, sensing means responsive to a temperature controlled by said evaporator, said sensing means being in a normal condition when said temperature controlled by said evaporator is above a predetermined temperature and being in another condition when said temperature controlled by said evaporator is below a predetermined temperature, means for opening said first shut-off valve and for closing said second shut-off valve when said sensing means is in its normal condition, and means for opening said second shut-off valve and for closing said first shut-off valve when said sensing means is in said other condition, whereby, when said stopstart means is in its normal condition, said compressor runs continually and the mass-rate of flow of refrigerant through the compressor is less when valved off from said evaporator than when passing through said evaporator.

6. In a refrigeration system having a normally continuously operating compressor, drive means for said compressor, stop-start means for said drive means which is normally operable to cause said compressor to be actuated, a condenser, flow restricting means, an evaporator, and conduit means for directing a refrigerant from the discharge of the compressor sequentially through the condenser, the flow restricting means, the evaporator and back to the suction of the compressor, said condenser, said flow restricting means, said evaporator and said conduit means being effective, when said stop-start means is in the normal condition and said compressor is driven by said drive means, to provide a predetermined rate of mass flow of refrigerant through said evaporator, the improvement comprising: a check valve in said conduit means between the discharge of said compressor and said condenser, a first shut-ofi valve in said conduit means downstream of said evaporator for preventing flow of refrigerant through said evaporator, lby-pass conduit means for directing refrigerant from the discharge of the compressor ahead of said check valve to the suction side of the compressor downstream of said first shut-off valve, said by-pass conduit means including pressure restricting means effective to limit the rate of mass flow to said compressor substantially below the predetermined rate of mass flow which normally passes to said compressor through said flow restricting means, a second shut-off valve in said by-pass conduit means, sensing means responsive to a temperature controlled by said evaporator, said sensing means being in a normal condition when said temperature controlled by said evaporator is above a predetermined temperature and being in another condition when said temperature controlled by said evaporator is below a predetermined temperature, means for opening said first shut-off valve and for closing said second shut-off valve when said sensing means is in its normal condition, and means for opening said second shut-off valve and for closing said first shut-off valve when said sensing means is in said other condition, whereby, when said stop-start means is in its normal condition, said compressor runs continually and the mass rate of flow of refrigerant through the compressor is less when valved off from said evaporator than when passing through said evaporator.

7. The refrigeration system of claim 6 wherein said first shut-off valve is closed for a period of time while said second shut-off valve is closed and before said second shut-off valve is opened to cause said compressor to evacuate refrigerant from between said shut-off valves on the suction side of the compressor to -between said check valve and said first shut-off valve and thereby cause a decrease in the mass of refrigerant circulated through the compressor when said second shut-01f valve is opened.

8. The refrigeration system of claim 6 wherein said check valve and said second shut-off valve are located closely adjacent the discharge of said compressor and whereby the mass of refrigerant in the system between the compressor discharge and said check valve and second shut-off valve is kept as small as possible, so that the References Cited by the Examiner UNITED STATES PATENTS 2,865,181 12/1958 Anderson 62- 199 MEYER PERLIN, Primary Examiner. 

1. IN A REFRIGERATION SYSTEM HAVING A NORMALLY CONTINUOUSLY OPERATING COMPRESSOR, DRIVE MEANS FOR SAID COMPRESSOR, STOP-START MEANS FOR SAID DRIVE MEANS WHICH IS NORMALLY OPERABLE TO CAUSE SAID COMPRESSOR TO BE ACTUATED, A CONDENSER, FLOW RESTRICTING MEANS, AN EVAPORATOR, AND CONDUIT MEANS FOR DIRECTING A REFRIGERANT FROM THE DISCHARGE OF THE COMPRESSOR THROUGH THE CONDENSER, THE FLOW RESTRICTING MEANS, THE EVAPORATOR AND BACK TO THE SUCTION OF THE COMPRESSOR, SAID CONDENSER, SAID FLOW RESTRICTING MEANS, SAID EVAPORATOR, AND SAID CONDUIT BEING EFFECTIVE, WHNE SAID STOP-START MEANS IS IN THE NORMAL CONDITION AND SAID COMPRESSOR IS DRIVEN BY SAID DRIVE MEANS, TO PROVIDE A PREDETERMINED PRODUCT OF THE DIFFERENTIAL PRESSURE ACROSS THE COMPRESSOR TIMES THE RATE OF MASS FLOW OF REFRIGERANT THROUGH THE COMPRESSOR, THE IMPROVEMENT COMPRISING: BY-PASS CONDUIT MEANS FOR DIRECTING REFRIGERANT FROM THE DISCHARGE SIDE OF THE COMPRESSOR AHEAD OF THE EVAPORATOR TO THE SUCTION OF THE COMPRESSOR BY-PASSING THE EVAPORATOR, SENSING MEANS RESPONSIVE TO A TEMPERATURE CONTROLLED BY SAID EVAPORATOR, SAID SENSING MEANS BEING IN A NORMAL CONDITION WHEN SAID TEMPERATURE CONTROLLED BY SAID EVAPORATOR IS ABOVE A PREDETERMINED TEMPERATURE AND BEING IN ANOTHER CONDITION WHEN SAID TEMPERATURE CONTROLLED BY SAID EVAPORATOR IS BELOW A PREDETERMINED TEMPERATURE, FLOW DIVERTING MEANS HAVING A NORMAL CONDITION, FOR COMMUNICATING REFRIGERANT FROM THE DISCHARGE OF THE COMPRESSOR THROUGH SAID EVAPORATOR AND HAVING ANOTHER CONDITION FOR SUBSTANTIALLY SHUTTING OFF FLOW OF REFRIGERANT THROUGH SAID EVAPORATOR AND DIVERTING THE FLOW THROUGH SAID BY-PASS CONDUIT MEANS, SAID FLOW DIVERTING MEANS BEING IN THE NORMAL CONDITION WHEN SAID SENSING MEANS IS IN ITS NORMAL CONDITION AND BEING IN ITS OTHER CONDITION WHEN SAID SENSING MEANS IS IN ITS OTHER CONDITION, AND MEANS EFFECTIVE WHEN SAID FLOW DIVERTING MEANS IS IN ITS OTHER CONDITION AND SAID STOP-START MEANS IS IN THE NORMAL CONDITION AND SAID COMPRESSOR IS DRIVEN BY SAID DRIVE MEANS TO REDUCE THE PRODUCT OF THE DIFFERENTIAL PRESSURE ACROSS THE COMPRESSOR TIMES THE RATE OF MASS FLOW OF REFRIGERANT THROUGH THE COMPRESSOR SUBSTANTIALLY BELOW THE PREDETERMINED PRODUCT. 